<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;

        }
        .box{
            height: 600px;
            background: plum;
            box-sizing:content-box;
            position: relative;
        }
        .box1,.box3{
            width: 200px;
            height: 100%;
            position: absolute;
            top: 0;
        }
        .box3{
            right: 0;
            background-color: rgb(129, 147, 245);
            
        }
        .box1{
            left: 0;
            background-color: aqua;
        }
        .box2{
            width: 100%;
            height: 100%;
        }
    </style>
</head>
<body>
    <div class="box">
        <div class="box1"></div>
        <div class="box2"></div>
        <div class="box3"></div>
    </div>
</body>
</html>